Patent GB-986677-A (GB)
Title: Electronic switching circuits
IPC: H03K17/58
Filed: 1961-09-29
Abstract: 986,677. Semi-conductor switching circuits; pulsing radio frequencies. INTERNATIONAL BUSINESS MACHINES CORPORATION. Sept. 29, 1961 [Oct. 5, 1960 (2)], No. 35079/61. Headings H3R and H3T. A switching circuit comprises two negative resistance elements connected in series and so biased that an input pulse of predetermined polarity applied across the elements changes the state of at least one of the devices to produce an output. An AND circuit, Fig. 2, for three condition signal, i.e. positive, zero or negative, comprises two tunnel diodes 30, 32 connected in series between bias sources 36, 38. With zero input at both inputs 46, 48 or one positive and one zero inputs, both the two diodes are in their low voltage state, and the output is zero. Application of two positive inputs causes the potential at point 58 to rise sufficiently to switch diode 30 to its high voltage stage and produce a positive output at terminal 66. Application of at least one negative input will switch diode 32 to give a negative output. In an OR circuit, Fig. 3 (not shown), the diodes 52, 56 and resistors 50, 54 are interchanged and the polarity of the diodes reversed. In an INVERTER, Fig. 6, four tunnel diodes 80, 82, 84, 86 are connected in series and are so biased that with a zero at input 96 diodes 80, 86 are in their low voltage state, and diodes 82, 84 in their high voltage state. The potentials at nodes 110, 112 are equal and opposite and produce zero output at 115. Application of a positive input to terminal 96 switches the state of diodes 80, 82 thus producing a difference between the potentials at nodes 110, 112 resulting in a negative output. Conversely a negative input will switch diodes 84, 86, resulting in a positive output. The circuits may be re-set by means of battery 70 and switch 72. If only positive pulses are to be inverted, diodes 84, 86 and the associated resistors may be omitted, Fig. 8 (not shown). In a modified positive inverter, Fig. 9, oppositely poled tunnel diodes 20, 22 are employed, the bias sources being appropriately connected. With zero input both diodes are in their low state, and a positive input at terminal 33 switches both to their high state producing a decrease in the potential at the output. The circuit may be modified for negative-going inputs by reversing the diodes and the bias potentials. A bipolar arrangement may be made by combining positive and negative circuits, Fig. 10 (not shown). The circuit of Fig. 9 may be used for AND or OR operation by connecting a number of inputs in parallel. In a circuit for producing short output pulses, Fig. 15, the arrangement of Fig. 9 is modified by the addition of delay lines 71, 73. Positive-going input pulses switch the state of diodes 20, 22 to produce an output pulse the duration of which is rapidly terminated by the reflected wave from the transmission lines switching the diodes back to their low state. In a further arrangement, Fig. 12, application of an input signal to the series connected tunnel diodes 20, 22 switches diode 22 to an unstable state in which the circuit will oscillate at a frequency determined by the inductances and capacitances in the circuit.